Three Bald Mice: The Link Between Behavioral Disorders and the Immune System

A recent study confirms the cause-effect relationship between problems in the immune system and the development of mental illness. Nobel Prize winning geneticist, Mario Cappecchi, and his team, linked a deficiency of microglial cells with Trichotillomania, an impulse control disorder that causes people to pull out their hair. In his experiment, Cappecchi performed bone marrow transplants on “hair pulling” mice. It was reported that within four months of the transplants, the mice no longer had the disorder. Consequently, healthy mice given bone marrow from affected mice developed the behavioral disorder.

The hair pulling in the mice was discovered to be caused by a deficiency of microglia in the brain. Microglia are located throughout the brain and spinal cord and play a major role in the immune defense of the central nervous system. They are responsible for locating damaged neurons as well as fighting off infections that go past the blood-brain barrier. The deficiency of microglia is said to be caused by a mutant Hox8 gene. The Hox8 gene is responsible for some of the development of the body and the organs. Since the microglial cells originate from the bone marrow and migrate towards the brain later on, it is the only group of cells in the brain that have this gene, and is suggested to be very important for the development of the brain.
Scientists were aware of the link between the immune system and mental illness for a while now. People diagnosed with psychiactric disorders such as bipolar disorder, schizophrenia, and depression often had problems with their immune system. This discovery, however, suggests a cause-effect relationship with problems in the immune system and psychiactric disorders. As Ghosh says, “Apart from the fact that this is the world’s first reported behavior transplant, this finding is an important landmark in our understanding of the genetic basis of behavior.” This opens a whole range of possibilities as scientists are able to apply the knowledge they know about the immune system discover causes for psychiatric disorders and also find ways to treat these illnesses with immuno-based therapy.